This invention relates to a discharge lamp lighting apparatus using semiconductor switch elements to supply power to a lighting circuit, which detects an anomaly involved in power supply.
To detect an anomaly concerning power supply in a system using a discharge lamp, for example, the following modes are known:
(I) Mode in which an input current supplied from a power supply to a lighting circuit (so called, ballast circuit) is directly detected and whether or not an anomaly occurs is determined; and
(II) mode in which an anomaly detection circuit is placed in a lighting circuit and detects an input current or its equivalent signal, whereby whether or not an anomaly occurs is determined.
However, the circuit modes in the related arts involve a problem about a power loss, costs, etc.
For example, in mode (I), occurrence of a power loss to detect a current flowing into a current detection element introduces a problem and in mode (II), addition of the anomaly detection circuit to the lighting circuit results in an increase in the number of parts, a rise in costs, complication of the configuration, etc.
If a mechanical switch of a relay, etc., is used for switch means in the discharge lamp lighting apparatus in the related art, there is a problem of limiting the anomaly detection method.
It is therefore an object of the invention to decrease a power loss and suppress a rise in costs in anomaly detection of a discharge lamp lighting apparatus.
To the end, according to the invention, a discharge lamp lighting apparatus comprises: a lighting circuit for lighting a discharge lamp upon reception of power supply from a DC power supply; a switch control circuit being placed between the lighting circuit and the DC power supply, which relays a power supplied from the DC power supply to the lighting circuit when the discharge lamp is lit; a circuit for supplying power to the lighting circuit through a semiconductor switch element placed in the switch control circuit, detecting a part of the current flowing into the semiconductor switch element, and comparing it with reference values, thereby detecting an anomaly in the lighting circuit or the discharge lamp is placed in the switch control circuit.
Therefore, according to the invention, a part of the current flowing into the semiconductor switch element is detected, whereby an anomaly can be detected and thus a power loss is lessened and an anomaly can be detected in the switch control circuit and thus the configuration is simplified and the circuit required for detecting an anomaly need not be placed in the lighting circuit.